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Патент USA US3068851

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Dec. 18, 1962
L. RoBBlNs ETAL
HYDRAULIC PRESSURE SYSTEM
Filed Jan. 13, 1961
QQ.
NN Sm
3,068,841
United States Patent Gtiîce
3,068,841
Patented Dec. 18, 1962
2
1
The invention includes an arrangement in which the
3,068,841
HYDRAULIC PRESSURE SYSTEM
Leo Robbins and Jack Bendror, Brooklyn, NX., assign
ors to Robbins & Bendror Associates Inc., New York,
N .Y.
Filed Jan. 13, 1961, Ser. No. 82,503
21 Claims. (Cl. 121-38)
This invention relates in general to a hydraulic pres
sure system and in particular to a new and useful hy
draulic press including an automatic arrangement for
rapidly advancing a ram toward a workpiece under low
actuating ñuid is sucked into the master cylinder by move
ment of the master piston by the pressure of the Huid
acting on the hollow slave piston. Thus a small quan
tity of ñuid and small pumping capacity is required to
maneuver the ram into an operating position while the
master piston is actually sucking large quantities of ñuid
through a suitable connection through the one end of the
master cylinder to the ñuid reservoir.
A feature of the invention is that the ram may be
operated automatically to advance the ram and upon the
ram encountering a major resistance force such as the
workpiece to be operated upon, the »tluid pressure is
power and low pumping volume requirements and for
automatically directed into the master cylinder and
eiîecting full force against the workpiece after the ram
15 against the master piston to eiîect the exertion of a large
is positioned in contact therewith.
compression force by the ram.
At the present time, hydraulic presses include, in most
A further feature or" the construction is that a low
instances, a single cylinder construction for advancing
capacity control valve may be employed to effect both the
the ram under the force of ñuid to pressurize one side of
advancing and the reversing movements of the ram. This
a piston connected to the ram. A disadvantage in a sin
gle cylinder construction is that a large horsepower re 20 control valve is not required to handle the Íluid which is
displaced by the master piston during its movements.
quirement for pumping the ñuid to advance the ram is re~
Instead, the valving arrangement includes means to con
quired to act against the large area piston, even though
the force of the ram is not being applied to a workpiece.
nect the master piston to a reservoir upon initiation of
return movement of the ram by directing pressurized ñuid
The area of the piston must be designed suiliciently
large to eiîect a large enough force for effecting sutiicient 25 into the hollow slave piston at a location between the
end wall of the master cylinder and the interior wall
pressing action on the workpiece, but the ram itself could
be advanced by a smuch smaller sized piston area member
while it is maneuvered to and from the workpiece.
In some instances, hydraulic pressure systems include a
of the master piston. The only electrical or manual con
trol required is one four-way valve which permits pres
surizing of the interior of the slave piston at one side of
small sized so-called slave cylinder for the purposes of 30 the master piston end wall and the simultaneous pres
surizing of one side of the master piston after the force
moving the ram backwardly and forwardly before it con
of the workpiece has been encountered, and for alterna
tacts the workpiece. Such systems include a control for
tively directing the pressure» to the interior of the slave
switching to a large size piston for effecting a large force
piston on the opposite side of the end wall of the master
on the workpiece by the ram.' Such systems have the ob
cylinder for the return movement of the ram. The valve
vious disadvantage that they require a duplication of the
also includes means for connecting the side of the slave
hydraulic pressure lines and there is a diñîculty in locating
piston which is not pressurized to a reservoir when the
the slave cylinderso that the force which it exerts on the
other side is pressurized and vice versa.
ram will act in a uniform axial direction so that the ram
Thus, the invention provides an unusual hydraulic
will not be misaligned during its movement. A very
important disadvantage of the use of a master piston 40 pressure system for a ram which makes it possible to
manipulate the ram by displacing a very small quantity
for effecting ram force on the workpiece and the slave
of control fluid and by expending a very small amount of
piston for advancing the ram is that the control valving
horsepower in pumping such tluid. Besides the fact that
to switch from the pressurizing of the slave cylinder to
it is not necessary to pump a large quantity of iluid inthe
the'pressurizing of the master piston must be sutiiciently
large to accommodate the displaced fluid from the master 45 manipulation of the master cylinder which exerts the
major pressure force on a workpiece, the invention pro
cylinder. This, of course, results in a large expenditure
vides a system which is much simpler from prior art
for valving and associate piping and the requirement for
constructions, particularly in respect to the amount of
large horsepower motor to operate the pump, since it is
parts and conduits required and in respect to the control
necessary to handle at least some portion of the liquid of
the master cylinder even though a small size slave cylin 50 valves which are necessary.
Accordingly, it is an object of this' invention to provide
der is operating to maneuver the ram into position.
an improved hydraulic pressure system.
In accordance with the present invention there is pro
A further object of the invention is to provide a hy
vided a combination master and slave cylinder construc
draulic press including a combination master cylinder and
tion which includes a relatively small diameter slave cylin
piston construction in which/the slave piston is made
der having side walls which are slidable in an end wall
hollow and has its walls in «an end wall of the master
of the main or master cylinder and which forms at its
cylinder for reciprocation therein, and including improved
inner end the master piston which reciprocates within the
vmeans for manipulating the ram under the control of
master cylinder. The center of the master cylinder in
the slave piston and for automatically switching to actu
cludes a cylindrical portion in which there is drilled a
passage for conducting ñuid under pressure to a location 60 ation of the master piston upon contact by the ram of
the workpiece or load.
'
between the interior face of the master piston and an in
A further »object of the invention is to provide an im
terior slave cylinder dividing wall formed as an extension
proved hydraulic control system for a hydraulic press in
of the end Wall of the master cylinder and within the
cluding means for rapidly advancing the ram by the dis
hollow slave piston. The pressure which is built up
within the interior of the hollow pressure slave system 65 placement of a small quantity of control lluid.
A further object of the invention is to provide a high
causes movement of a ram attached to the end of the
piston by the pumping of a relatively small quantity of
speed hydraulic press including means for advancing the
ñuid which acts against the relatively small area which is
exposed within the hollow slave piston and which acts
against the end wall of the master cylinder and the interior
wall of the master piston to advance the hollow slave
ram thereof by the displacement of a small quantity of
control ñuid and the expenditure of a relatively small
amount of power, and further including automatic means
for increasing the pressure force applied on the ram after
it contacts a workpiece.
piston and the ram.
'
3,068,841
3
4
A further .object Yof the invention is to provide a hy
draulic press Which is simple in desi-gn, rugged in con
i
A combination plunger 'and piston member generally
designated 68 lincludes a plunger portion 70 which is
slidable in the portion 64 and a piston portion 72 which
The various features of novelty which characterize the
is slidable within a slightly Vlarger diameter portion 74.
invention are pointed out with particularity in the claims 5 The diameter of the piston portion 72 is larger than the
annexed to and forming a part of this spe'ciñcation. For
plunger diameter '70 for the purpose to be setrfrorth more
a better understanding of the invention, its operating
fully hereinafter.
p
advantages and specific objects attained by its use, refer
The piston is -biased by means of a spring ‘76 against
ence should be had to the accompanying drawing and
an end wall 7S which is provided with openings which
descriptive matter in which there is illustrated and de
lead to passages V80 which connect via a check valve 82
scribed a preferred embodiment of the invention.
to the conduit 656' and a passage 84 which connects to
In the drawings:
a central passage 86 in which a pilot rod memberSS isV
FIG. 1 is a top plan view of a hydraulic press con
slidable. There is a clearance between »the «piston Jpor- Y
structed in accordance with the invention;
tion 72 and the cylindrical walls 90 of the 'control valve
FIG. 2 is a somewhat schematic transverse horizontal
member 54 for the purpose of permitting the passage of
section through the combination master and slave cylinder
' pressurized control fluid therearound las will be described
and control valve indicated in FIG. l and showing the
more fully hereinafter (see FIG. 3).
various hydraulic `conduit connections; and
The conduit 60 joins to a lflexible conduit 92 which con
FIG. 3 is a vertical section taken on the line 3_3 of
nects into the hollow slave piston 32 between the exterior
FIG. 2 on a somewhat exaggerated scale.
end of the cylindrical extension 26 and the end wall 44V
Referring to the drawings in particular, the invention
thereof. Each of the conduits 92 and 6d leads to a com
embodied therein includes ahydraulic press comprising
bined conduit 94 which connects to the four-way sole
a rigid rectangular frame generally designated 10 which
noid actuated valve 62. The conduit 28 also Vconnects
includes a front wall 12 against which is rigidly fastened
to the four-way solenoid actuated valve 62.
a clamping jaw i4 of the hydraulic press.
The opposite side of the valve .'62 is connected through
A combination master and slave cylinder construction
a conduit 96 which leads to a pump 98 which takes suc- Y
generally designated 16 is provided with a reinforced end
tion in a fluid reservoir 100. A pump motor-V102 is pro
vided to rotate the pump ‘98 to pressurize the conduit 96
wall or head 11S which is rigidly fastened to an end wall
and the pressure of the ñuid delivered by the pump
20 of the frame 10. ln accordance with the invention,
the combination masterV `and slave cylinder and piston 30 through >the conduit 96 Ymay be selectively connected to
the conduit 28 or to the conduit 94. Four-way valve 62V
member 16 includes a relatively large diameter master
cylinder 22 formed as an extension of the head 18 and
is also >connected by way of a conduit 104 to a fluid
reservoir 106. It should be appreciated that the reser
terminating in an opposite end wall or head 24 which is
secured to the wall 1S by means of elongated stud or bolt
voirs indicated as 5S, 100 and 106 may be and normally
members 25. The head 1S includes a central elongated 35 are one and the same reservoir.
The operation of the device is as follows: When Vit is
cylindrical extension 26 which extends from the head
struction and economical to manufacture.
.
desired `to advance the ram 46 in a direction of the arrow
18 in the direction of end wall 24. The end wall or
108 a lsolenoid plunger 112 is actuated by a suitable elec
head 1S and the lcylindrical extension 26 Áare `provided
trical control to cause the pressurized `conduit 96 to be
withY a passage 2S -for conducting control ñuid through
an opening 30 which is located approximately «in the-same 40 communicated to the >conduit 94 and to simultaneously
connect .the conduit 28 to the reservoir 106 via the con
plane as the Vend Wall 24.
duit 104.
The construction includes -a combination hollow slave
piston and master piston assembly generally designated
After the valve Vis :thus positioned„pressure is admitted
through conduit 92 to the hollow slave piston 32 at the
32 which includes a cylindrical wall portion 34 which is
slidable between suitable seals 36 and 3S in the end Wall 45 location Ybetween the widened end 40 of the cylindrical
extension 26 and the end wall 44vto cause a buildup of
24 »and lateral annular extension 40 of the cylindrical
pressure therein and movementof the wall `44 away from
extension 26, respectively.
the extension 26 to displace the ram l46 in the direction of
The cylindrical walls 34 define a slave hollow piston
the arrow 108. During this time,.conduit 28 is exposed
or Ycylinder -member which has one wall closed Vby a
master piston 42 in an opposite end closed by a wall 50 through the opening 30 to the interior of the slave piston
32 to a chamber 110 on the opposite side of the widened
44 which is connected to a ram 46. The ram 46 is
adapted to be displaced by thehydraulic fluid in direc-V
portion 40 of the cylindrical extension 26 and the fluid
tions toward and away from the clamping jaws for oper~
pressure is relieved in the chamber 110. This permits
the control fluid to lbe bled through the passage 28 to the
Y ation on a workpiece positioned Ibetween the-clamping
jaws and the ram.
In the embodiment shown, the press 55 valve V62 and `conduit 104 to the reservoir 106.
_. is a bookbinding press.
' Y.
G
Thus
rapid advanceV of the ram 461is accomplished by means '
The master piston 42 is of a larger diameter than the
cylindrical walls 34 and includes a sealing ring-48 to
of the displacement of a'small quantity of fluid ¿in a hol
low sla-ve piston >32.
valve member Agenerally designated 5?, which is providedV
chamber 64 of the control valve 54 and through conduit
50 tothe ychamber 52. Thus, a large quantity of liquid
`is displaced by the `movement of the master piston 42
but this liquid` does not have Vto be separately pumped
It should be appreciated that when the Vram y46 is dis
maintain Ya liiuid tight seal during the reciprocation of
Vthe piston-42 in the cylinder 22. A conduit 50 ‘is pro 60 placed >by the pressurizing of the slave piston 32 in the
chamber formed .between the end 4of the cylindrical ex
vided for directing Aiiuid into the space 52 between the
tension 26 and the walls44, >the master piston 42 is also
Vend wall» 18 and the master pistonV 42. The conduit 50
moved within the cylindrical walls 22. This movement
alsojprovides la passage for relieving the pressure during
of the master piston 42 causes the sucking in of Yiiuid
the‘return movement of the piston 42.
'
from the reservoir 58 through the conduit 56 into the
A Vfeature of the invention isv the provision of a novel
withan opening at one end 56 which is connected to an
oil reservoir 5S and a small size opening 60 which is
connected to' a four-way solenoid control valve generally
designated 62,.Y An intermediate opening 64 is provided
and lit does not pass through the control -valve 62.
Y Yin,Y the control valve member '54 in alignment with theV
YWhen the ram 46 meetsresistance such -as by contact
opening 50 in the' end wall 1S. The interior of the valve
ing a- workpiece, the pressure in' conduits 92, k94 and 60
builds up toa value suíîicient to Vpush the pilot rod 88 in
' control member 54 Vis provided with a bore portion 64V
' of larger internal'diameter than the conduitV 56 and a
~
the ,control valve 54 to the left asY indicated in FIG. 2.YY 1
beveled portion 66 connecting conduit 56 and portion 64. 75 This causes movement of the plunger/17,0 to the left as "Y
3,068,841
5
6
.
viewed in the drawings until the whole plunger and piston
assembly 63 moves suliiciently to close the opening 50.
At this time pilot rod 88 has moved sufficiently to the
left to uncover the passage S4. The pressurized ñuid
from the conduit 60 passes through the passage 84 and
around the piston 72 to a- space within the valve between
the piston 72 and the plunger 7i), while it continues to
urge the combination piston and plunger member 68 to
the left to close thus preventing any escape of Huid.
The plunger portion '7d moves sufficiently to uncover
the passage 5@ and permit it to communicate with the
passage 68 through the passage 34 to cause the fluid to
enter the chamber 52 and displace the master piston 42
to cause the exertion of a large amount of force by the
ram 46 on the workpiece. Once the ñuidpressure within
the chamber 52 is increased, the plunger 7@ is urged
against the beveled portion 66 with an increasing force
to tightly close oñ the conduit 56 and prevent leakage
42, it may be of much smaller and less costly construc
tion than similar valves in prior art hydraulic systems
of this character. The advancing and retracting move
ment by the slave hollow piston is very rapid.
While a specific embodiment of the invention has been
shown and described in detail to illustrate the application
of the invention principles, it will be understood that the
invention may be embodied otherwise without departing
from such principles.
What is claimed is:
1. A hydraulic system comprising a supporting frame,
a master cylinder having end walls of relatively large
diameter and being supported on said frame, a combina
tion slave cylinder and master piston member including
a hollow cylindrical wall portion of smaller diameter than
the internal diameter of said master cylinder slidable in
an end wall of said master cylinder, said master cylinder
including end wall means dividing the interior` of said
slave cylinder portion, a master piston formed at one end
of oil to the reservoir 5S.
When it is desired to retract the ram 46 the plunger 20 of said slave cylinder of substantially the same diameter
as the internal diameter of said master cylinder, and
1312 of the valve 62 is actuated to connect the conduit 28
means to selectively pressurize said slave cylinder on alter
to the pressure line 96 and the conduit 94» to the reservoir
nate sides of said dividing wall means without pressurizing
M6. The pump 98 therefore directs duid through the
said master cylinder to cause relative movement of said
conduit 28 and out the opening 39 to pressurize the
chamber lli). Since the cylindrical extension 26 and its 25 slave cylinder in respect to said end wall means in accord
flange portions 46 are stationary, the master piston 42 is
ance with the _side thereof which is pressurized.
- 2. A hydraulic system for a press and the like compris
displaced by the action of the fluid within the smaller
annular area defined at one end of the chamber liti.
ing a master cylinder of relatively large diameter, said
master cylinder having spaced end walls, one of said end
Since the conduit 92 and the conduit 61B are connected
to the reservoir, the pressure is relieved on the other 30 walls having a central extension extending outwardly
side of the cylindrical extension in the slave hollow piston
therefrom toward the opposite end wall, a combination
32 and return movement may be accomplished. How
master piston and slave cylinder member slidable in an
ever, as long as the plunger '743 closes the opening to the
end wall of said master cylinder and extending around
conduit 56, the oil in the chamber 52 is forced to iiow
the extension portion of the opposite end wall, said ex
through the chamber within the walls of the cylindrical 35 tension portion including a widened portion substantially
valve 54 between the plunger 70 and the piston 72,
dividing the interior of said slave cylinder, and pressure
around the piston and through the check valve S2 to the
conduit means connected directly to said slave cylinder
conduit 6i). The clearance between the piston 72 and
on each side of said widened portion without communi
the cylindrical walls 90 is arranged to offer some resist
cating with said master cylinder, whereby said cylinder is
ance to the large flow of oil from the chamber 52. Some 40 movable relatively to said end wall of said master cylinder
pressure will therefore be maintained in the chamber 52
in accordance with which side of the interior of said
which will push back the combination plunger and pis
slave cylinder in respect to said widened portion is pres
ton rods 68 and to first close and thereafter open the port
surized.
64. This occurs because the piston 72 is of a larger di
3. A hydraulic system for a press and the like accord
ameter than the plunger 70 and the pressure acting against 45 ing to claim 2, wherein said extension portion of said
the face of the piston overcomes the pressure acting
one end wall includes an internal conduit for directing
against the face of the plunger. The spring 76 aids in
fluid to the interior of said slave cylinder on one side of
moving the combination plunger and piston member 68
the widened portion which divides said slave cylinder.
to the right but it is gradual until the plunger 7 0 uncovers
~4. A hydraulic system for a press according to claim
the port 64. After the port 64 is partly opened, the pres 50 2, including a second conduit connected to said master
sure in the chamber 52 immediately drops as the conduit
cylinder on the opposite side of said master piston from
513 communicates with the conduit S6 and the spring 76
said slave cylinder, means to selectively pressurize the
is therefore able to return the combination piston and
conduits on alternate sides of said widened portion, and
plunger member 68 to the position indicated in FIG. 2.
means connected to said pressurizing means and respon
Thus, it can be seen that the ram 46 may be moved 55 sive upon the buildup of pressure to a predetermined
or manipulated into a position by the displacement of a
amount to connect said second conduit to said pressurized
small quantity of fluid requiring a pump of much smaller
means.
'
horsepower than if the master piston 42 had to be dis
5. A hydraulic system for a press according to claim
placed by directing fluid against its face during the manipu
2, wherein said means to connect said second conduit to
lation stage of the rarn. The invention includes means 60 said pressurizing means includes a control valve, said
for automatically causing the pressurizing of the master
control valve having an intermediate conduit connected
piston 42 when the load is encountered by the ram, caus
to said second conduit, reservoir means connecting one
ing a raising of the pressure in the conduits which feed
end of said control valve, pressurized ñuid means con
the slave portion. Since the operation of the device de
necting the opposite end of said control valve, said control
pends on the pressures within the connecting conduits 65 valve having a displaceable valve member therein movable
and the associated portions of the control valve, the equip
upon increase of pressure in said pressure conduit means
ment requires very little maintenance and very little atten
to close said reservoir means from communication with
tion in its operation. The device may be operated with
said second conduit.
a single electrically actuated four-way control valve for
6. In a hydraulic system including a master cylinder
effecting forward or reverse movement of the ram 46 as 70 of relatively large diameter having closing head portions
desired. The overall construction is very inexpensive to
at each end, one of said head portions having a central
manufacture and the saving in horsepower requirements
opening, a central portion extending interiorly of the other
of said head portions to Isaid central opening, including
is considerable. Due to the fact that the four-way sole
noid control valve only handles a small quantity of liquid
a widened outer end, a combination master piston and
and not the full quantity of liquid displaced by the piston
slave cylinder member slidable on said central portion in
3,068,841
7
8
sealing >engagemnt with the end Ahead of said master cyl
inder and the widened outer end of said central portion,
15. A hydraulic system according to claim~»14, includ
a ?irst conduit deñned in said central portion and extend
ing a second passage formed in said valve wall and con
nected to said second conduit and the intermediate cham
ing through the connected head and in communication
with the interior of said slave cylinder on the interior
ber of said valve, said second passage having a check
valve therein.
side Vof said widened end portion, a second conduit con
16. A control valve for a fluid system comprising `a v
valve body having an opening> at one end, a hollow in
nected to said slave cylinder on'the opposite side of said
widened -end portion, a liquid reservoir, a liquid pressure
line, and valve means for selectively connecting said pres
terior chamber portion in alignment with said opening, a
first connection intermediate the length of said body `to
sure line to said iirst conduit and connecting said second 10 said central chamber, a second connection connecting the
conduit to said liquid reservoir and for thereafter connect
opposite end of said separate chamber, a combination
ing said second conduit to said liquid pressure means and
plunger and piston member slidable in said chamber andV
said first conduit to said liquid reservoir.
Y 7. A hydraulic system according to claim 6, wherein
said Valve means is a four-way solenoid actuated valve.
including a plunger portion, a piston portion and a pilot
rod disposed adjacent said piston portion extending to .said
second connection, said pilot rod Vbeing displaceable'uponv
8. A hydaulic system according to claim 6, including
increase in pressure in »saidf second connection ,to dis
means connecting said master cylinder on the opposite
place said combination plunger and piston rod member,
side of said master piston from said slave cylinder portion
said plunger portion being Vof a size to close said open
to said liquid reservoir, and valve means in said'connec
ing and having a skirt portion movable to open and close
tion Vincluding means automatically operable to connect 20 said first connection, said plunger being moved to an ex
said master cylinder to said liquid reservoir upon the pres
treme vposition to completely close said opening and the
surizing of said first conduit.
»
communication of said ñrst and second connections on
9. A hydraulic system according to claim 8, wherein
the interior of said valve.
said valve means includes means to'connect said master
,
' ~
Y
17. AV control valve for the fluid system according to
cylinder to said liquid pressure line upon the building up 25 claim 16, wherein said piston portion is of larger .diam
eter than said plunger portion >but is not as large in diam-iV
of pressure _within said second conduit to a predetermined
amount.
Y
eter as the bore of the interior walls of said Valve body
c
10. A hydraulic system according to claim 9, wherein
whereby iiuid may bypass annularly aroundV said piston
said valve means includes a third conduit connection to
from said íirst connection to said second connection.
18.V A control valve for a lluid system according to
claim 17, including a passage defined in said valve body
said master cylinder between said master piston and the 30
Y adjacent head, and a plunger displaceable `between a posi
tion closing said third conduit and to a position connecting
connected between said second connectionand the interiorV
said third conduit to said ñuid pressure means.
chamber of said valve, said passage having a check valve
' 1l. A hydraulic system according to claim 6, including
therein.
,
a Vthird conduit connected to said master cylinder between 35
19. A control valve for a liuid system according vto
said master piston vand the adjacent head and connected
claim 18, including a passage deñned between said second
to said second conduit, a control valve disposed in said
third conduit, said liquid reservoir being connected to
connection and central chamber of said valve body.
v20. A control Valve for a fluid system according toV
said valve means at one end thereof, said `connection to
claim 16, wherein said valve body includes ,acentral .pas
40
said îliquid reservoir being in communication with said
sage for said pilot rod, a first passage communicating
third conduit >through the interior of one end of said
with said second connection and said central chamber, 2a
valve, said third conduit ,and second conduit being in
second passage communicating with said passage lforsaid
communication at the opposite end of said valve, and a
pilot rod and said central chamber, said pilot rod being
plunger member >slidable to close the communication be
displaceable toV uncover said Yiirst passage .to Ípermit fluid
45
tween said third condnit and said reservoir in one extreme
connection between said second connection and said cen
position and in an opposite extreme position to close the
tral chamber whereby to displace said plunger ¿to initially
communication between said third conduit and second
cover said ñrst connection and thereafter to cover `said
conduit and to open the communication between said
Vthird conduit and said reservoir.
V12. VA hydraulic system according to claim 11, wherein 50 21. A control valve for a iluid system according to
said plunger means includes a slidable member having l claim 16, wherein the annular clearancebetween said
opening.
interior walls of said valve.
,
c
Y
14. A hydraulic system according toV claim 13„wherein
v
'
‘
valve body isV of an amount to create'suii‘icient resistance
connection to said reservoircand having a cylindrical skirt
said combination plunger and piston member includes a
piston formed at one end having a larger diameter than
said plunger member but Ybeing of less diameter than the
'
‘
piston portion of the bore of the interior walls> of saidV
Y a plunger at one .end movable against a seat to close said
portion simultaneously uncovering ?said third conduit for
communication with said second conduit,
13. A hydraulic system according to claim 12, wherein
'
to the flow ofV fluid to .cause a back pressure sufficient to
55 force said plunger portion to open the connection be
tween the chamber of the master cylinder and the liquid
reservoir, said plunger portion being of a smaller eiîec
tive area than'said piston portion.
60
kReferences Cited in the ñle of this patent
said valveV has walls having a port extending from a lo
UNITED STATES PATENTS
cation adjacent said >third conduit «connection to a loca-l
Hottel ______ __ _______ ___ Jan. 6, 1931
1,788,298
tion intermediate the ends of said Valve, said piston por
Ernst ________ ___ _____ __ May ’1, ‘1934
tionlbeing disposed in a chamber Vat the end of said pas 65 ' 1,956,758
2,293,334
Ernst
_ _____ __ _____ _____ Aug. 18, 1942
sage, and a pilot rod adjacent said piston portion and
2,437,077
Cole __ ____ ___ ________ __ Mar. 2, V1948
displaceable upon increase in pressure in `said second
2,502,547
Adams et al ____________ __ Apr. 4, V1795()
conduit to shift said combination plunger and piston mem
'2,636,406 n
Salter ____________ ____ __ Apr. 28, 1953
ber to cover the connection to saidreservoir.
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